1. Field of the Technology
The present disclosure relates to methods of processing high strength, non-magnetic corrosion resistant alloys. The present methods may find application in, for example, and without limitation, the processing of alloys for use in the chemical, mining, oil, and gas industries. The present invention also relates to alloys made by methods including the processing discussed herein.
2. Description of the Background of the Technology
Metal alloy parts used in chemical processing facilities may be in contact with highly corrosive and/or erosive compounds under demanding conditions. These conditions may subject metal alloy parts to high stresses and aggressively promote corrosion and erosion, for example. If it is necessary to replace damaged, worn, or corroded metallic parts of chemical processing equipment, it may be necessary to suspend facility operations for a period of time. Therefore, extending the useful service life of metal alloy parts used in chemical processing facilities can reduce product cost. Service life may be extended, for example, by improving mechanical properties and/or corrosion resistance of the alloys.
Similarly, in oil and gas drilling operations, drill string components may degrade due to mechanical, chemical, and/or environmental conditions. The drill string components may be subject to impact, abrasion, friction, heat, wear, erosion, corrosion, and/or deposits. Conventional alloys may suffer from one or more limitations that negatively impact their performance as drill string components. For example, conventional materials may lack sufficient mechanical properties (for example, yield strength, tensile strength, and/or fatigue strength), possess insufficient corrosion resistance (for example, pitting resistance and/or stress corrosion cracking), or lack necessary non-magnetic properties to operate for extended periods in the down-hole environment. Also, the properties of conventional alloys may limit the possible size and shape of the drill string components made from the alloys. These limitations may reduce the service life of the components, complicating and increasing the cost of oil and gas drilling.
It has been discovered that during warm working radial forging of some high strength, non-magnetic materials to develop a preferred strength, there may be an uneven deformation or an uneven amount of strain in the cross-section of the workpiece. The uneven deformation may be manifest, for example, as a difference in hardness and/or tensile properties between the surface and the center of the forging. For example, observed hardness, yield strength, and tensile strength may be greater at the surface than at the center of the forging. These differences are believed to be consistent with differences in the amount of strain developed in different regions of the cross-section of the workpiece during radial forging.
One method for promoting consistent hardness through the cross-section of a forged bar is to use an age hardenable material such as, for example, the nickel-base superalloy Alloy 718 (UNS N07718) in the direct aged or solution treated and aged condition. Other techniques have involved using cold or warm working to impart hardness to the alloy. This particular technique has been used to harden ATI Datalloy 2® alloy (UNS unassigned), which is a high strength, non-magnetic austenitic stainless steel available from Allegheny Technologies Incorporated, Pittsburgh, Pa. USA. The final thermomechanical processing step used to harden ATI Datalloy 2® alloy involves warm working the material at 1075° F. to an approximately 30 percent reduction in cross-sectional area on a radial forge. Another process, which utilizes a high grade alloy steel referred to as “P-750 alloy” (UNS unassigned), sourced from Schoeller-Bleckmann Oilfield Technology, Houston, Tex., is generally disclosed in U.S. Pat. No. 6,764,647, the entire disclosure of which is hereby incorporated by reference. The P-750 alloy is cold worked to about a 6-19 percent reduction in cross-sectional area at temperatures of 680-1094° F. to obtain relatively even hardness through the cross-section of a final 8-inch billet.
Another method for producing a consistent hardness across the cross-section of a worked workpiece is to increase the amount of cold or warm work used to produce a bar from the workpiece. This, however, becomes impractical with bars having finished diameters equal to or greater than 10 inches because the starting size can exceed the practical limits of ingots that can be melted without imparting problematic melt-related defects. It is noted that if the diameter of the starting workpiece is sufficiently small, then the strain gradient can be eliminated, resulting in consistent mechanical properties and hardness profiles across the cross-section of the finished bar.
It would be desirable to develop a thermomechanical process that could be used on high strength, non-magnetic alloy ingots or workpiece of any starting size that produces a relatively consistent amount of strain through the cross-section of a bar or other mill product produced by the process. Producing a relatively constant strain profile across the cross-section of the worked bar also may result in generally consistent mechanical properties across the bar's cross-section.